The present invention relates to a relatively small rotary liquid pump intended for use as an automobile fuel pump, particulary to a rotary positive displacement pump of pin roller type (hereinafter referred to as a vane pump).
A conventional vane pump of this kind is shown in FIG. 1. In the figure, reference numeral (1) is the armature of a motor to drive the pump, (1a) is the driving shaft of the motor (1), and (2) is a pump base made of a bowl with a wall (2a) to serve as the flat surface of the pump chamber, a guide hole (2b) to serve as a delivery outlet, and a bearing (3) embedded in pump base to support the driving shaft (1a). Reference numeral (4) denotes a rotor firmly mounted on the driving shaft (1a) and provided with a plurality of clearance grooves (4a) equally spaced and opened to the periphery thereof. (5) denotes free moving rollers each of which is inserted into the clearance grooves (4a) of the rotor (4). (6) denotes the pump housing to form the cylindrical side wall of the pump chamber. The rotor (4) and the rollers (5) are so placed in the pump housing (6) as to permit them to rotate freely therein. The center of the inner diameter of the pump hosing (6) is eccentrically positioned a certain distance (A) off the center of the driving shaft (1a) as shown in FIG. 2. The radius of the inner diameter of the pump housing (6) is slightly larger than the sum of the distance (A) and the radius (R) of the rotor (4), i.e. A+R+.alpha.. The pump chamber formed is such that the rotor (4) comes closest to the inner cylindrical wall of the pump housing at the point (6b) of the wall and it is separated by a gap of 2(A+.alpha.)=B at the point (6a) of the inner cylindrical wall. (7) is a pump case comprising a wall (7a) to provide a flat surface, an inlet groove (7b) for suction, and a hose joint (7d) with a clearance hole (7c) communicating with the inlet groove (7b) to surve as an intake. (8) is a metallic cylinder to accommodate the pump system therein and fitted with an exit pipe (10) via a packing (11). The exit pipe (10) has the outlet (9) at the other end. (12), (13), (14) are O-rings for hermetic sealing.
The following are the details of the construction and materials of the components to form the pump chamber. The pump base (2) and the pump case (7) are fabricated by die casting of aluminum die casting alloy. The walls (2a) and (7a) to provide flat surfaces are given surface treatment (anodizing) to form a film with abrasion resistance thereon after their machining finish. The rotor (4) and rollers (5) are fabricated by machining a piece of carbon steel to a shape close to the one shown in the drawing, quenching it to increase its wearing resistance, and grinding it for surface finishing. The pump housing (6) is fabricated by punching a sheet of carbon steel to form, quenching it to increase its wearing resistance, and grinding its inner cylindrical wall and both end surfaces.
The operation of the vane pump thus constructed will be described. When an electric power is fed to the armature (1) of the motor, the rotor (4) firmly mounted on its driving shaft (1a) rotates counterclockwise with the rotation of the shaft (1a). As the rotor (4) rotates, the rollers (5) fitted in the clearance grooves (4a) are forced to rotate counterclockwise by centrifugal force while they are kept in contact with the inner cylindrical wall of the pump housing (6). The description of the changes in the situation of the rollers (5) in the pump chamber as the rotor (4) rotates will be given in detail. A space of the pump chamber defined by one of the rollers (5) located at the point (6b) on the inner cylindrical wall at the start of pump operation will gradually increase as the rotor rotates thereby to have a negative pressure therein.
Consequently, fuel will be sucked through the clearance hole (7c) as the intake connected to the inlet groove (7b). When the rotor (4) moves further and passes the point (6a) on the inner cylindrical wall, the space in the pump chamber starts to decrease thereby gradually compressing the fuel. With the compression, the fuel reaches the duct (2b) for delivery outlet, moves forward inside the metallic cylinder and is delivered through the outlet (9). In this way, the well-known pumping operation is performed.
In the conventional vane pump thus constructed, when the rotor (4) and rollers (5) rotate, the both ends of the rotor (4) come in contact with the flat surface wall (2a) of the pump base (2) and the flat surface wall (7a) of the pump case (7), respectively, at the same time, the clearance grooves (4a) keep in contact with the outside of the rollers (5). The rollers (5), while in contact with the walls of the clearance grooves (4a), contacts at the outer wall with the cylindrical wall of the pump housing (6). Both ends of the rollers (5), like those of the rotor (4), comes in contact with the flat surface walls (2a) and (7a). Therefore, the known vane pumps tend to have the contact surfaces of their components worn out as a result of the contact friction between the parts of the pump components. This tendency becomes remarkable when a pump is operated in a dry condition for many hours or after use over a long period of time. The abrasion leads to an increase of current a reduction in rotational speed, and a decrease in internal pressure and quantity delivered. This will eventually bring about a failure of the fuel supply to an internal combustion engine. However, the conventional vane pumps as described above in regard to the components have all of the rotor (4), rollers (5) and pump housing (6) precision machined such as grinding machined after quenching for increased abrasion resistance. Therefore, it has disadvantages including a high cost due to the difficult machining and the heavy weight. The vane pump base (2) and the vane pump case (7) are also machined to produce the flat surface walls (2a) and (7a) after die casting. This is another disadvantage contributing to the high cost.